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#[derive(Debug, Copy, Clone, PartialEq)]
pub struct Operator {
token: char,
operation: fn(f64, f64) -> f64,
precedence: u8,
is_left_associative: bool,
}
#[derive(Debug, Copy, Clone)]
pub enum Token {
Operator(Operator),
Num(f64),
LParen,
RParen
}
impl Operator {
fn token_from_op(token: char, operation: fn(f64, f64) -> f64, precedence: u8, is_left_associative: bool) -> Token {
Token::Operator(
Operator {
token,
operation,
precedence,
is_left_associative
}
)
}
fn operate(self, x: f64, y: f64) -> f64 {
(self.operation)(x, y)
}
}
fn main() {
let input = "1 + 5 * 6 + 2";
println!("{}", input);
let input = input.replace(" ", "");
let lexed = lexer(&input);
let postfixed = to_postfix(lexed.unwrap());
let evaled = eval_postfix(postfixed.unwrap());
println!("{:?}", evaled);
}
fn lexer(input: &str) -> Result<Vec<Token>, String> {
let mut num_vec: String = String::new();
let mut result: Vec<Token> = vec![];
for letter in input.chars() {
match letter {
'0'...'9' | '.' => {
num_vec.push(letter);
},
'+' | '-' | '/' | '*' | '^' => {
// parse num buf
let parse_num = num_vec.parse::<f64>().ok();
if let Some(x) = parse_num {
result.push(Token::Num(x));
num_vec.clear();
}
// finish
let operator_token: Token = match letter {
'+' => Operator::token_from_op('+', |x, y| x + y, 2, true),
'-' => Operator::token_from_op('-', |x, y| x - y, 2, true),
'/' => Operator::token_from_op('/', |x, y| x / y, 3, true),
'*' => Operator::token_from_op('*', |x, y| x * y, 3, true),
'^' => Operator::token_from_op('^', |x, y| x.powf(y), 4, false),
_ => panic!("unexpected op whuuu"),
};
result.push(operator_token);
},
'(' => {
// parse num buf
let parse_num = num_vec.parse::<f64>().ok();
if let Some(x) = parse_num {
result.push(Token::Num(x));
result.push(Operator::token_from_op('*', |x, y| x * y, 3, true));
num_vec.clear();
}
if let Some(x) = result.last() {
match x {
Token::RParen => {
result.push(Operator::token_from_op('*', |x, y| x * y, 3, true));
},
_ => {}
};
}
// finish
result.push(Token::LParen);
},
')' => {
// parse num buf
let parse_num = num_vec.parse::<f64>().ok();
if let Some(x) = parse_num {
result.push(Token::Num(x));
num_vec.clear();
}
// finish
result.push(Token::RParen);
}
' ' => {}
_ => {
return Err(format!("Unexpected character: {}", letter))
}
}
}
let parse_num = num_vec.parse::<f64>().ok();
if let Some(x) = parse_num {
result.push(Token::Num(x));
num_vec.clear();
}
Ok(result)
}
fn to_postfix(tokens: Vec<Token>) -> Result<Vec<Token>, String> {
let mut postfixed: Vec<Token> = vec![];
let mut op_stack: Vec<Token> = vec![];
for token in tokens {
match token {
Token::Num(_) => {
postfixed.push(token);
},
Token::Operator(current_op) => {
while let Some(top_op) = op_stack.last() {
match top_op {
Token::LParen => {
break;
}
Token::Operator(top_op) => {
let tp = top_op.precedence;
let cp = current_op.precedence;
if tp > cp || (tp == cp && top_op.is_left_associative) {
postfixed.push(op_stack.pop().unwrap());
} else {
break;
}
}
_ => {
return Err(format!("Unexpected match branch part 2"))
}
}
}
op_stack.push(token);
},
Token::LParen => {
op_stack.push(token);
},
Token::RParen => {
let mut found: bool = false;
while let Some(top_op) = op_stack.last() {
match top_op {
Token::LParen => {
let _ = op_stack.pop().unwrap();
found = true;
},
_ => {
postfixed.push(op_stack.pop().unwrap());
}
}
}
if found == false {
return Err(format!("Mismatched parentheses part 2"))
}
}
}
}
while let Some(op) = op_stack.pop() {
postfixed.push(op);
}
Ok(postfixed)
}
fn eval_postfix(postfixed: Vec<Token>) -> Result<f64, String> {
let mut num_stack: Vec<f64> = vec![];
for token in postfixed {
match token {
Token::Num(n) => {
num_stack.push(n);
},
Token::Operator(op) => {
if let Some(n2) = num_stack.pop() {
if let Some(n1) = num_stack.pop() {
num_stack.push(op.operate(n1, n2))
} else {
return Err(format!("Too many operators, Too little operands"))
}
} else {
return Err(format!("Too many operators, Too little operands"))
}
}
_ => {
return Err(format!("Yo nibba how did this get here"))
}
}
}
if num_stack.len() == 1 {
Ok(num_stack.pop().unwrap())
} else {
Err(format!("Parser Error"))
}
}
|
